Synthesis, crystal structure, spectroscopic characterisation and magnetic properties of [Cu-2(BIBM)(2)(C2O4)(2)]center dot 4H(2)O (BIBM = bis(2-imidazolyl) bis(methoxycarbonyl)methylmethane)

The structure and spectroscopic and magnetic properties of bis(mu -1,2,3-ox alato)bis[bis(2-imidazolyl)bis(me methylmethane]dicopper(LI) tetrahydrate a re described. The compound is built of centrosymmetric neutral dimeric [Cu- 2(BIBM)(2)(C2O4)(2)] entities linked through hydrogen bonds involving water molecules and oxalate groups. In the dimeric unit the two centrosymmetrica lly related copper - which are involved in CuN2O2O2' chromophores lying in an elongated octahedral environment - are bridged through the oxalate group which acts in a bidentate-monodentate (mu -1,2,3) fashion. Both electronic and EPR spectra are indicative of an essentially d(x2-y2) ground state for the copper(II) ions. Magnetic susceptibility measurements in the range 1.8 -200 K show very weak antiferromagnetic exchange between the copper(II) ion s (2J = -0.35 cm(-1)). This feature is discussed on the basis of the relati ve orientation of the coordination polyhedron around the metal atom and the bridging network. (C) 2001 Published by Elsevier Science B.V.